This is because you are connecting from a different host, OGo only accepts
connections from localhost per default. For deployments it works like this:
<pre>
/----------------\ Internet /--------\ local /-----\
| Browser/Client |   &lt;-&gt;    | Apache |  &lt;-&gt;  | OGo |
\----------------/          \--------/       \-----/
</pre>
So you should setup Apache for proper forwarding of requests, see the <a
href="/en/install/apache13.html">install instructions</a>. Using Apache in 
front of OGo is recommended for a whole lot of
reasons (eg OGo itself does not speak full HTTP/1.1, but rather lets Apache do
the hard work ;-).
<br /><br />
That being said, you can configure OGo which hosts to allow access from by using
the "WOHttpAllowHost" default, eg:
<pre>
Defaults write OpenGroupware WOHttpAllowHost \
  '(localhost, myhost.mydomain)' 
</pre>
alternatively you can use
<pre>
  -WOHttpAllowHost '(localhost, "myhost.mydomain")'
</pre>
when starting OGo from shell.